Computer networks for use in a business environment continue to require more storage. Typically, such enterprises employ a centralized data storage system, and the computer network includes various personal computers, laptops, etc. that communicate over the network with the data storage system. The data storage system typically includes one or more servers that control the storage of information on and the retrieval of information from dedicated data storage resources, such as hard disk drives, magnetic or optical disks. As the demand for storage continues to increase, the storage capacity of the centralized storage system is becoming larger and larger, and the systems are becoming more and more complex and costly to operate. The complexity and costs are increased by the additional requirement for redundant storage capabilities.
Some enterprises have migrated storage resources to a storage area network (SAN). A SAN is a specialized, high-speed computer network that is typically used to attach computer systems or servers (commonly referred to as “hosts”) with little or no local storage to back-end storage devices that provide the bulk of storage and the shared storage. The primary purpose of the SAN is to transfer data between the hosts and the storage devices. A SAN typically includes a communication infrastructure that provides physical connections and a management layer that organizes the connections, storage elements, and computer systems, so that data transfer is secure and robust. SANs are typically, although not necessarily, identified with block input/output (I/O) services. SANs provide an alternative to traditional dedicated connections between servers and local storage elements, as well as any restrictions to the amount of data that a server may access. Instead, a SAN provides the flexibility of networking to enable one server or many heterogeneous servers to share a common storage unit, which may include a storage controller and many storage devices, such as, for example, disk, tape, optical, or other storage devices or systems. Despite the advantages of SAN-based solutions, they remain prohibitively expensive for many smaller enterprises or in small exchange deployments.
Another storage solution involves Direct Attached Storage (DAS) in which all the storage is seen as local by each server and is under the direct control of storage controllers integrated with the servers. The storage may be physically inside the server or outside the server or any combination of the two, but the critical distinction of a DAS system is that the controller of such storage is seen as local for each server and is not shared with other servers. The main advantage of this approach is that its cost is significantly lower than a SAN, at least for small configurations. However, the DAS approach also has disadvantages. For instance, the main limitation is that the storage is only local and cannot be shared across servers, thus creating major limitations in terms of fault tolerance. If a server dies, all its storage dies with it and there is no way to access the data any longer. In contrast, the SAN approach allows the same data to be accessed by other servers that can provide (at a high cost) a convenient failover mechanism.
Despite the many advantages and the commercial success of redundant storage systems and SAN-based storage solutions, there remains a need in the art for more cost-effective redundant storage systems.